In an aircraft, the outer skin is spaced from the walls and ceiling of a passenger cabin (or other compartment), and the gap is at least partially filled with an insulation layer or blanket. The insulation layer is typically formed from a waterproof material. During a flight, liquid from moist air can condense against the skin, particularly at the top of the fuselage, and freeze during cruise. During decent, this frozen liquid can thaw and drip back down towards the cabin. Because the insulation blanket is waterproof, the condensate can typically flow along the insulation blanket and drain into the bilge. However, at some locations, structures and/or supports can protrude through the insulation blanket. For example, the supports that hold monuments and stowage bins to the crown extend from the structure at the skin, through the insulation blanket, and into the cabin. The insulation blankets come with predefined holes for the supports to extend through the blanket. The holes are lined, and there may be a gap defined between the inner surface of the hole and the support. When liquid thaws, it can drip down through the hole and into the cabin.
Further compounding the issue of holes predefined in the blanket, sometimes during maintenance and/or repair the insulation blankets are dislocated from their original intended position and because the blankets are generally flexible with little shape memory, they will not usually return to their intended position naturally. This dislocation of the blanket will sometimes result in a deterioration of the blanket's ability to properly channel liquid moisture towards the bilge at the bottom of the plane fuselage thereby causing liquid moisture to drip towards the passenger cabin.
Previous attempts at controlling undesirable moisture from dripping into the passenger cabin also include using moisture control felt. While the use of the moisture control felt provides an incremental improvement over not using felt at all, it has been discovered that on flights of long duration and/or with many passengers and/or in high humidity environments the moisture control felt can become saturated and at least partially ineffective, resulting in moisture dripping into the passenger cabin.